Conventionally, there is a countermeasure against EMI (hereinafter, referred to as “EMI countermeasure”) for a multipolar connector. In the EMI countermeasure, a shell of a cable-side connector which is configured as a multi-polar male connector (multipolar plug), and that of a board mounted (apparatus-side) connector which is configured as a multipolar female connector (multipolar receptacle) functioning as a fitting counter are used for covering circumferences of fitting portions of the connectors, and formed by metal plates to have a shielding property, respectively. When the cable-side connector and the board mounted connector are fitted to each other, the shells are electrically coupled to each other. In order to reduce the cost and size of the multipolar connector, each of the shells is formed into a tubular shape by applying a pressing process such as a punching process or a bending process on a metal plate. Therefore, the shell has a seam joint which is formed with being centered at the center line so that the strength balance of the shell is maintained (see. Literature 1).